Calls for effective international action to tackle the use of tax havens by wealthy individuals have followed the leak of 11 million confidential documents from a Panamanian law firm, which is accused of helping clients launder money, dodge sanctions and evade tax.

Initial analysis of the documents, leaked to the German newspaper Sueddeutsche Zeitungand then shared with 107 media organisations in 78 countries, has identified 12 current or former heads of state using offshore havens, and 61 people linked to current or former world leaders.

Among the reported disclosures so far gleaned from the 40 years of documents from the secretive law firm Mossack Fonseca is a suspected $2 billion money-laundering ring run by a Russian bank and said to involve close associates of President Vladimir Putin. The Kremlin has dismissed the claim as an attempt to smear the president.

Meanwhile, Icelandic Prime Minister Sigmundur Gunnlaugson was facing resignation calls on Monday after the documents appeared to show an undeclared offshore interest linked to his wife’s wealth, while the leaks also contained details of secret offshore companies linked to the families and associates of Egypt’s former president Hosni Mubarak, Libya’s former leader Muammar Gaddafi and Syria’s President Bashar al-Assad.